The present invention relates to a charged particle beam projection aligner having a position detector using a light beam and more particularly to the projection aligner having the position detector which is able to detect marks on a semiconductor wafer such as an IC, LSI, etc., having multi-layers for wiring by using the light beam and align the position of a semiconductor wafer with high accuracy.
When an alignment mark on the semiconductor wafer is clearly exposed on a surface of the wafer, the alignment mark is easily detected by scanning with the charged particle beam which is used for exposing the wafer. But, recently, IC, LSI, etc., devices on the semiconductor wafer are constructed with many wiring layers, and the alignment marks are buried in the wiring layers, making it difficult for the charged particle beam to distinguish the alignment marks buried in the wiring layers from other portions. Therefore, it becomes impossible to detect the alignment mark correctly by scanning the alignment marks with the charged particle beam.
On the other hand, since the light beam easily passes through a transparent portion of the many wiring layers and distinguishes the buried alignment marks from other portions of the wiring layers, the alignment marks are easily detected by scanning with the light beam. For these reasons, the charged particle beam projection aligner generally has the position detector which detects the alignment marks on the semiconductor wafer by using a light beam for aligning the position of the wafer.
The U.S. Pat. No. 4,698,513, the Japanese Patent Laid-Open No. 1-184825 (1989) and the Japanese Utility Model Laid-open No. 1-67733 are cited as examples of such device.
But the conventional technique shown in the above examples has the following drawbacks.
A light projection device for projecting the light beam and the detector for detecting the light beam of the charged particle beam projection aligner are apart from the charged particle beam device and are disposed in a very narrow space between the semiconductor wafer and an objective lens which projects the charged particle beam onto the semiconductor wafer and a fiducial mark on the XY table. Therefore, the light beam is projected with an extremely inclined angle onto the surface of the semiconductor wafer from the light projection device disposed at the side of the objective lens, and it becomes difficult to focus the light beam correctly onto the surface of the semiconductor wafer and XY table and to align the semiconductor wafer with high accuracy (because of a convex and concave surface of the semiconductor wafer and XY table).